USB Printer Share Switch: Simple Circuit Design

Description

This straightforward apparatus facilitates the sharing of a single USB device, such as a computer printer or an external flash drive, memory card reader, or scanner, between two computers. A rotating selector allows the user to designate the machine intended for utilization with the USB device, while two light-emitting diodes demonstrate the currently selected computer.

The most prevalent approach to distributing a USB printer across two systems involves utilizing one machine as a print server. However, this isn't always practical because it necessitates the server computer remaining operational to enable printing.

Picture of the project:

This can prove to be a significant inconvenience if one simply desires to quickly activate the other computer and initiate printing. Furthermore, both computers must be connected to a network, either through a hub/router or directly via an ethernet crossover cable.

An alternative method is to employ a dedicated USB print server. Nevertheless, as previously stated, such a device must also be connected to an ethernet network, along with the computers. These devices also require their own power source, typically costing more than $100 and representing excessive expenditure when only a single USB printer needs to be shared between two computers for infrequent use within a domestic setting.

Parts layout:

It is in this instance that this uncomplicated apparatus proves valuable. It essentially comprises a two-way switch housing that enables the manual routing of a USB printer to either of the connected computers. Switching is accomplished using a rotary selector, while two light-emitting diodes on the front panel signify which computer is currently connected to the printer.

This methodology offers several key benefits. Firstly, no network connection is required between the two computers. Secondly, printing can be initiated from either machine, regardless of the other computer being powered off. And thirdly, the device does not necessitate a power supply.

Circuit diagram:

The circuit employs switch terminals S1a-S1c to select either USB connector CON1 or CON2 and connect its pins through to CON3. The fifth terminal (S1d) selects either light-emitting diode LED1 or LED2, to indicate which computer has been selected.

A dedicated integrated circuit (IC) – specifically, a 74HC542 – is utilized to implement the switch matrix. This IC functions as a multiplexer, allowing the rotary switch to control the selection of either the USB connector or the light-emitting diode, depending on the desired output. The IC’s inputs are connected to the rotary switch terminals, and its outputs are connected to the USB connectors and light-emitting diodes. This IC provides reliable switching functionality and isolation between the two circuits. This particular IC is commonly used in switching applications due to its low power consumption and robust performance.